Basically, FINRA is putting the kabosh on the use of social media by individual FA's. It requires the firm to establish policies for monitoring and approval of content, and no B/D is going to take responsibility for monitoring individual FA's social networking posts.
Now, I can see soem B/D's getting involved with social networking at the corporate level, and designing their own content for sites, but I doubt use will become widespread by individuals.
http://www.investmentnews.com/apps/pbcs.dll/article?AID=/20100125/FREE/100129938

No big deal. You can’t use Facebook etc for business use. You want to post your family pics or chat with your friends - fine. If you want to prospect, give finanicial advice, or recommend stocks on your myspace page you will have a problem.